This letter describes design and performance of small-size push-on type connectors. Considering bending and tensile stress applied to the push-on type coupling, the minimum dimensions of the coupling have been clarified. The constructed connectors for multimode fibers showed average insertion losses of 0.1-0.2 dB.

A GaAlAs/GaAs surface emitting (SE) injection laser with 6µm cavity length was directly modulated with a pulse width of 300 psec. Single longitudinal mode operation under this modulation condition was obtained and thus mode selectivity of the SE laser due to its large mode spacing was confirmed.

The frequency response of parametric modulation of semiconductor lasers is given by taking the lateral carrier diffusion effect into account. It is confirmed that the carrier diffusion affects to flatten the resonance peak, and overall modulation response is not changed so much.

This paper presents a design for a 1.55 µm, 450 Mbit/s high-sensitivity receiver, employing an InGaAs/InGaAsP/InP-APD and a high-impedance preamplifier with a GaAs MESFET front-end circuit. Studying Ge-APDs and InGaAs/InGaAsP/InP-APDs, it is confirmed that InGaAs/InGaAsP/InP-APDs are suitable for the wavelength region around 1.55 µm and transmission bit rates near 450 Mbit/s. Further studies on InGaAs/InGaAsP/InP-APDs confirm that they should be used in the lower multiplication reqion: e.g. less than 15. Using a InGaAs/InGaAsP/InP-APD and a high-impedance preamplifier, a receiver sensitivity of -42.9 dBm at a bit error rate of 10^-11 is realized. Applying this receiver with a high power optical source, a stable longitudinal spectrum distributed feedback laser diode (DFB-LD), a 450 Mbit/s transmission experiment over 210 km distance is successfully carried out.

This paper discusses the measurement results of atmospheric attenuation at 11 and 18 GHz obtained by a dual frequency sun-tracker. The performance of the sun-tracker and the measuring method of atmospheric attenuation by means of observating the solar radiation are described. The annual, seasonal and monthly variations of measured atmospheric attenuation for each frequency are clarified based on a statistical analysis of data measured over a period which continued for three years. As an outcome of the regression analysis concerning the relation between the measured atmospheric attenuation and the surface meteorological data, two models were obtained. The first gave rise to a single linear equation which has the water vapor density as a variable. The second model took into account the oxygen density as well as the water vapor density. Moreover, the precision of estimation which can be achieved in estimating the atmospheric attenuation from the surface meteorological data using these models was shown.

A radio acoustic sounding system (RASS) is used to remotely measure the atmospheric temperature profiles, since the speed of the acoustic pulse can be measured from the ground by means of a Doppler radar. A theoretical analysis on received signal characteristics of a RASS which uses acoustic pulse-modulated and radio continuous waves has been made by deriving the scattered field from weak refractivity variations produced by an acoustic pulse. The analysis has revealed the influence of horizontal winds for temperature measurement by a RASS as follows:
[1] The shift frequencies of return signals of a RASS coincide with Doppler frequencies only under low wind condition.
[2] The shift frequencies of return signals of a RASS coincide with acoustic frequencies transmitted under strong wind condition.
Measured results by a JRC RASS confirmed the results of the theoretical analysis.

Windows in rectangular waveguides are used frequently in microwave circuits. Capacitive or inductive windows have been studied in detail. Though the problems for the fields of these windows can be reduced to one-dimensional problems, the field of the resonance window is obtained by solving a two-dimensional problem. Thus the field of the resonance window is more difficult to obtain. Various characteristics of the resonance window in the rectangular waveguide have not been much studied analytically. A simple and approximate expression which was obtained experimentally for calculating the resonance frequency of the window is well known. The authors study the various characteristics of the resonance window by the variational method and Schwinger's transformation. We show an expression for susceptance of the window by these methods, and we can evaluate the resonance frequency and loaded Q numerically. These data by the numerical calculation are shown in figures, which may be useful to the design of microwave circuits. These data are compared to experimental data and theoretical values for windows of special cases. As a result, it is found that the data illustrated with the figures hold sufficient accuracy.

Bundle-integrated-guide (BIG) structure distributed-Bragg-reflector (DBR) lasers based on 1.5-1.6 µm GaInAsP/InP system are presented. The significance of this structure is the suitability for the planar fabrication process of integrated optical devices, such as DBR lasers, which comprise active and passive waveguide regions. The BIG structure enables easier fabrication of buried hetero-structure (BH) of such an integrated waveguide device. High coupling efficiency between those waveguides of 95-99 percent is theoretically available with sufficiently large tolerance in thickness and composition of waveguide layers. Devices with different lengths of the active region, such as 200 µm, 100 µm and 50 µm, were fabricated and tested both for DC operation and rapid direct modulation. Threshold current as low as 28 mA and output power of 6.5 mW/facet were obtained for BH-BIG-DBR lasers with 100 µm long and 3 µm wide active region. Side-mode suppression ratio (SMSR) of more than 32 dB was obtained at the bias current of 1.2 times the threshold and it was not much degraded by rapid direct modulation.

The surface structure of an artificial membrane composed of a Millipore filter and a synthetic lipid analogue, dioleylphosphate (DOPH), immersed in KCl solution changes when CaCl₂ concentration reaches a critical value. Using a photomultiplier mounted on the eyepiece of a stereoscopic microscope the structure change can be measured quantitatively as an intensity variation of reflected light of the membrane surface. Calcium ions decreased finally the intensity to more or less 50 % as compared with the original hydrophilic state whose solution was only KCl. However, the degree of structure change was dependent on following conditions: adsorbed DOPH densities, solution temperatures and pH values. On the other hand, using the light reflectance curves obtained from the structural observations, an unknown CaCl₂ concentration in a KCl solution can be detected. Since the reflectance curve shifts widely with various densities of DOPH adsorbed in the Millipore filter, it is possible to detect the CaCl₂ concentration of wide range. The detection range was from 0.1 to 50 mM CaCl₂.

This paper describes power feed techniques for telephone subscribers in a metallic two-wire digital subscriber loop system and optical fiber subscriber loop systems. In a metallic two-wire digital subscriber loop system, Digital Service Unit (DSU) and Digital Telephone (DTEL) are installed on the subscriber premises. The power consumption of the equipment increases compared with that of the conventional analog telephone. Therefore, it is difficult to feed sufficient power to the equipment using a conventional 48 V constant-voltage power supply. A constant current power feeding method from the central office is suitable because constant power can be obtained with little energy loss. A small-size and low-cost constant current converter has been developed. In optical fiber subscriber loop systems, it is difficult to feed the customer's equipment with power from the central office. Therefore, an uniterruptible DC power unit has to be installed on the subscriber's premises. The power unit is composed of sealed lead-acid batteries and a multi-input converter which has rectifier and DC-DC converter functions. This converter is very small and low-cost. The life of a sealed lead-acid battery can be prolonged by coating the outside of the battery container with aluminum or fluoric-resin film, and by optimizing the calcium content in the electrode grid alloy.